Mexico/Carribean for October half term?

HiI am planning a get away for myself and DH for a week and am wanting to know any recommendations. I have recently been to Cancun, but fancy Cozumel if I do return to Mexico. We are happy to give most things a go but with particular focus on a good beach, decent access to snorkling and other watersports. We aren't too bothered about luxury but have a decent budget.

It would be the end of October if we were to go - we are hoping that by then it is over. September would be right in the middle.I was at Cancun at a conference and am thinking that the area would be nice to take my DH as it seemed a shame (sort of) to not be able to share it with him.

Thanks! I fancy anywhere in the Carribean but in Mexico there are the options to see Chichen Itza and check out the sinkholes as well. The scary thing is is that it probably won't cost that much more than a term-time trip to Centre Parcs!

I think we will go for Playa del Carmen. I'm not fussed about luxury but want the option of going out on excursions. A nice beach for snorkling would be good. We will probably book a package option with extras.I was in Cancun for work and really fancy taking DH to the Carribean coast. It will be good to spend all day out on excursions rather than squeezed into the afternoons.

PS I can say that a nice beach and tropical weather IS conducive to research!

Thanks for the help guys - I will be officially booking this once all the tortuous expense claims have all been sorted. Cancun was good for conference but 5 hours on a coach to go anywhere interesting was a bit of a pita.